Brazing compositions having polyvinyl butyral as a binder



United States Patent 3,166,402 BRAZING COMPOSITIONS HAVING PQLYVINYL BUTYRAL AS A BINDER Jerome A. Berson, Madison, Wis, and Arthur T. Cape,

Monterey, Califi, assignors to Powder Melting Corporation, Monterey, Calih, a corporation of California No Drawing. Filed Sept. 24, 1963, Ser. No. 311,212 4 Claims. (Cl. 75-.5)

This invention relates generally to brazing compositions, but has reference more particularly to brazing compositions containing metallic brazing powders includ' ing those of the nickel-base type, manganese-base type, copper-base type, cobalt-base type, and copper.

The use of various binders to facilitate application of such powders to the parts to be brazed has heretofore been proposed, but in all cases, have proved objectionable for various reasons, including the following:

(a) The binders were not soluble in water, so that if used, they had to be dissolved in various solvents other than water, including potentially dangerous organic solvents.

(b) The binders were not entirely satisfactory, from the viewpoint of holding the particles of brazing powder together until they commenced to sinter and melt.

(c) The binders did not become completely volatilized or consumed or otherwise dissipated during the brazing operation, and left an ash or residue which materially hindered the uniform and free flow of the melted powder into the joints between the parts being brazed.

The present invention has as its primary object the provision of a brazing compositon consisting of a metallic brazing powder and a binder, which, while not soluble in water, forms a suspension in water, and holds the particles of brazing powder together until they commence to sinter and meld incidental to the brazing operation, and which becomes substantially completely volatilized, consumed or dissipated during the brazing operation, and leaves substantially no ash or residue which can hinder the uniform and free flow of the melted powder into the joints between the parts being brazed.

Another object of the invention is to provide a brazing composition of the character described, in the form of a flexible self-sustaining sheet, strip, film, ring, washer, wire, or similar form.

A further object of the invention is to provide a method of brazing in which a brazing composition of the aforesaid character is utilized.

Other objects and advantages of the invention will become apparent in the course of the following description of the invention.

In acocrdance with the invention, polyvinyl butyral is used as a binder or vehicle for metallic brazing powders, particularly powders of the types which have been described above, but it is to be understood that it may be used as a binder or vehicle for other types of brazing powders, with equally advantageous results.

Although polyvinyl butyral is not soluble in water, it does form a suspension in water, and the suspension may be mixed easily and uniformly with the powder and the mixture spread on a flat surface, and permitted to dry, or can be warmed to facilitate drying, and thereby formed into thin flexible sheets, in which the powder is uniformly distributed and locked or held, pending use of the sheet in a brazing operation.

In like manner, washers can be made by placing the mixture into annular shaped molds and drying it in the molds.

The amount of ployvinyl butyral in the mixture may be varied, but in general, we prefer to use a mixture consisting of three parts by weight of the brazing powder prevent adhesion of the mixture to the plate.

3,165,462 Patented Jan. 19, 1965 to one part by weight of an aqueous suspension containing about 32.5% polyvinyl butyral. This mixture will thus contain about 8% polyvinyl butyral and about 17% by weight of water. If all the water were to be evaporated from the mixture, in the process of drying the mixture,

the resultant brazing composition would contain about 90% by weight of powder and about 10% by weight of v polyvinyl butyral. However, it is necessary to retain some moisture or water in the brazing composition at all times in order to provide a self-sustaining flexible sheet of the character which has been described, and this moisture may vary from about .5 by weight of the sheet to about 5% by weight of the sheet.

The brazing composition, in the form of the dried or partially dried sheet, may be varied, so that it contains from about 5% to about 11% by weight fo polyvinyl butyral, about .5 to about 5% by weight of water, and the balance substantially all the brazing powder. This variation may be obtained in any desired manner, but it is most easily obtained by varying the amount of polyvinyl butyrl in the water suspension thereof.

A preferred example of such a brazing composition consists of about 8% polyvinyl butyral, about 2% water, and the balance essentially all a metallic brazing powder consisting of about 82% nickel, about 7% chromium, about 5% silicon, about 3% boron, and about 3% iron.

The mixture can be rolled out on a glass or polished steel plate, using a substance, such as silicone grease, to The sheets, after drying, may be used directly in the brazing of parts of stainless steel and heat-resistant alloys of the type known as super alloys.

They may, for example, be used directly in the brazing of honeycomb structures, in which case, they may be placed either on the honeycomb core or on the sheets or skins which are used to contain the core.

The assembly of the structure to be brazed and the brazing composition is held together by means of a fixture and the assembly is held in place by the polyvinyl butyral at least until it begins to sinter, and then melts and brazes. I

The use of polyvinyl butyral is advantageous because of its complete suspendability in water.

' the problems incidental to dissolving a binder or vehicle 'in potentially dangerous organic solvents.

The polyvinyl butyral binder holds the particles of brazing powder together until they commence to sinter and melt, and during the brazing operation, it becomes substantially completely volatilized or consumed, leaving virtually no ash or residue to hinder the uniform and free flow of the melted powder into the joints between the parts being brazed.

Other vinyl or polyvinyl compounds have been tried as binders, including polyvinyl acetate, polyvinyl butyraldehyde, polyvinyl butyral ether, polyvinyl methyl ether,

' vinyl halide polymers and polyvinyl ketals, but have proved objectionable for one or more of the reasons hereinbefore stated.

The invention is applicable mainly to .the brazing of parts of stainless steels and super alloys, but may be used for the brazing of other metals which are to be brazed or joined.

The metallic brazing powders which form the predominant constituent of the brazing compositions which are the subject of the present invention include powder of the nickel-base type, manganese-base type, copper-base type, cobalt-base type, and copper.

Among powders of the nickel-base type are those covered by A.M.S. specifications Nos. 4775, 4776, 4777 and 4778, and Coast Metals Nos. 50, 51, 52, 53, 54, 55, 56, and 59. Coast Metals No. 5 is representative of such This eliminates 22150 whereby to each other. p V V This application is va continuation-in-part of our application's, Serial No. 639,239,;now abandoned, and Serial No. ;8l3',066,"filed May114, 1959, now abandoned;

"'manganes'e base alloys,

powders, and has the following specificationor nominal composition: t

a Other elements 15 max;

7 Among powders of the manganese-base type is Coast Metals 'No. 62,'which consists of 63-67% manganese, 14-18% nickel-and 1418% cobalt.

Among powders of the copper-base type are Coast "Metals,1600-1700 Series, containing from 35 to 75% copper, about'3 to' 20% nickel, and the remainderessentially all manganese.

- Percent Nickel s1.0 s3.0 Chromium i. 6.5-7.5

Silicon, 4.0-5.0 1

Boron L 2.5-3.5 Iron 2.5-3.5

- Among powders-of the cobalt-base type are the various stellitealloys, the compositions ofwhich are well known. ,In using said composition, thefbrazing composition is -placed between the metallic surfaces to be brazed, and the surfaces and composition heated to a brazing temperature, which may vary from" about 1700 F. to about 'Hav-ing thus described our invention, We claim:

alloysfand'copper; v

effect brazing of said surfaces; to 1' 2, The method'of brazing which'comprises placing between metallic surfaces to be brazed a brazing composition consisting of from about 5% to about 11% polyvinylrbutyral, from about 1.5% to about 5%. by Weight of water, and the balance essentially all ametallic brazing powder selected from" the group consisting of nickel-base alloys, manganese-base alloys, copper-base alloys, cobalt-base alloys, and copper, and heating said i 7 surfaces and composition to a brazing temperature, Whereby to eifect brazing of said surfaces to each other.

Ai self-sustaining sheet for use in brazing,v said sheetgconsistingof from about 5% to about 11% by weight of polyvinyl butyral, from about ,.5%' to about 5 by Weight of water, and the balance essentially all a metallic brazing powder selected from the group consisting of nickel-base alloys, manganese-base alloys, cop per-base'all'oys, cobalt-base" alloys, and copper. v i V '14. The method of preparing a self-sustaining sheet for use in brazing, said method comprising the steps of pre- 7 paring a mixture consisting of an aqueous suspension of polyvinyl butyral and a 'meta'llicbrazing powder -selected from the group consisting of nickel-base alloys,

manganese-base alloys, coppenbase alloys, cobalt-base alloys, and coppen-forming saidmixture into a sheet,

and permitting waterto evaporate from said sheet to the extent that the sheetwill consist of from about 5% to about 11%. by weight of polyvinyl butyral, from about and the balance" 5% ;to about 5% by weight of water, essentiallyisaid brazing powder; 7 7

RefereneesCiteelin the file of this patent. I UNITEDQSTATES PATENTS 2,914,435 Wasserman Y Rankin "M ay 9, 1939 Nov. 24, 1950 

1. A BRAZING COMPOSITION CONSISTING OF FROM ABOUT 5% TO ABOUT 11% BY WEIGHT OF POLYVINYL BUTYRAL, FROM ABOUT .5% TO ABOUT 5% BY WEIGHT OF WATER, AND THE BALANCE ESSENTIALLY ALL A METALLIC BRAZING POWDER SELECTED FROM THE GROUP CONSISTING OF NICKEL-BASE ALLOYS, MANGANESE-BASE ALLOYS, COPPER-BASE ALLOYS, COBALT-BASE ALLOYS, AND COPPER. 